Metal cleaning compound



Patented Dec. 15, 1931 UNITED STATES GRINNELL JONES, CAMBRIDGE, MASSACHUSETTS METAL QLEANING COMPOUND No Drawing. Original application filed September 7, 1927, Serial No. 218,115. Divided and this application filed August 24, 1928. Serial No. 301,931.

This invention relates to improvements in metal cleaning and more particularly to the removal of tarnish from articles of silver.

Hitherto, one of the most widely used methods of cleaning gold or silver articles has been by the use of abrasives, either alone or incorporated in a paste or cloth by means of tallow or other grease. Such abrading process is necessarily slow and has the d1sadvantage of abrading or removing a portion of the metal surface as well as the tarnish. A further disadvantage resides in the fact that it is very diflicult or almost impossible to clean depressed portions of embossed or engraved articles.

Another method in wide use is that of dissolving the tarnish in strong, hot solutions of cyanides. Cyanides, as is well known, are extremely poisonous, and cannot be handled with safety in the ordinary household. Further, any carelessness in washing off the cleaned articles after treatment might result in the fatal poisoning of anyone using them. In addition, the well known solvent action of cyanides for silver, in the presence of air, is a factor to be taken into account.

The most commonly used method is to immerse the article to be cleaned in a boiling alkaline solution, such as a solution of sodium carbonate, sodium bicarbonate or trisodium phosphate, contained in an aluminum pot or like vessel. Ordinary salt may be added to speed up the electrochemical action. The article to be cleaned must be in electrical contact with the aluminum, either directly or through another piece of metal, so that an electric current can flow from the metal to be cleaned to the aluminum and back to the metal through the electrolyte. This combination forms a short-circuited electrolytic cell in which the aluminum dissolves electrolytically and thosulfide of the tarnished metal is reduced electrochemically to the metal. The sulfide ion liberated unites with the hydrogen set free toform gaseous hydrogen sulfide. Hydrogen sulfide has an ofiensive odor. This old method of cleaning silver leaves the metal with a dull or unpolished surface and injures the aluminum pot used.

It is an object of this invention to provide a composition of matter which is adapted to remove tarnish from metals, and one which does not require the articles to be cleaned to be immersed therein.

It is a further object of this invention to provide a composition of matter which is adapted to remove tarnish from metal and to simultaneously neutralize or combine With the hydrogen sulfide gas liberated.

Another object of this invention is to provide a composition of matter which does not comprise alkalies or other caustic or poisonous substances and is adapted to detarnish metals.

Yet another object of this invention is to provide such a composition of matter as a vendible article, either as a powder or paste.

I accomplish these and other desirable objects by providing a composition of matter comprising a finely divided metal, which is electropositive with respect to the metal to be cleaned, in combination with a substantially anyhydrous acid or acid salt, preferably with any or all of a neutral salt, an antiodor, an abrasive, put up either as a powder or a paste, and adapted to be activated when wet.

In the manufacture of the composition comprising my invention I use a metal which is sufficiently electropositive with respect to the metal to be cleaned as to have a detarnishing action thereon. I have found that to secure the best results the metal should be' finely divided, or pulverized if possible. As the result of protracted experiments, I have found that the following metals are suitable for use in a composition for detarnishing silver or other tarnishable metals or alloys, when taken in conjunction with the acids and acid salts to be hereinafter referred to. The metals, in the order of their reducing power, are: ma esium, zinc, manganese, cadmium, iron an aluminum. It will, of course, be readily. understood that other metals havin the desired characteristics may be used, an the foregoingare iven merely by wa of illustration. The factors of availabi it of materials, cost, ease of processing (grin ing, mixing), stability, reducing power, and hardness enter into the choice of the particular metal to be used, and such choice will be readily made by those skilled in the art for an glven set of conditions.

11 combination with any of the foregoing metals, I make use of a suitable acid or acid salt. As I have mentioned above, the particular acid or acid salt chosen must be readily soluble in water, non-poisonous, non-hydroscopic, commercially available at a moderate price, and of moderate strength. If it is to be part of the powder or paste sold, it must be in the solid form. If it is intended for household use it may be a liquid. For use in owder form acid salts are preferred, since t eir solutions combine good electrical conductivity with moderate acidity and therefore give rapid detarnishing action without excessive generation of heat.

After numerous experiments, I have found that the following compounds give ver satisfactory results in conjunction wit the metallic components heretofore described.

These compounds are given by way of ill'ustration only, as it will be readily apparent that I may use any compound having like characteristics without departing from the spirit of my invention. The pre erred compounds are as follows: citric acid, tartaric acid, benzoic acid, salicylic acid, sodium acid citrate, potassium acid citrate, sodium acid tartrate, potassium acid tartrate and monosodium dihydrogen phosphate.

I have also found that the acid or acid salt may be omitted entirely from the composi-' tion in order to avoid any. premature reaction between the components. In this case the user can obtain the desired result by adding any appropriate acid solution to the composition at the time of use. I find that vmegar, lemon juice, sour milk and like acidulated compositions are suitable for use with the finely divided metals above mentioned. These acid materials are available in every household, and are of relatively low price.

In preparing my improved composition. I first reduce the individual components to any desired state of subdivision by appropriate mechanical or chemical means. The desired quantity of the separate ingredients is then taken and the whole is intimately mixed in a suitable machine such as a ball mill, or the like. To prevent any undesirable premature reaction between the components, I carry out the grinding and mixingpractically any cheap, non-poisonous, nonydroscopic, easily soluble neutral salt may be used. Sodium chloride is the cheapest and most readily available, although I secure efficient results by the use of sodium citrate,

sodium tartrate, or sodium sulfate. It will be readily apparent that any salt having the desired characteristics can be made use of in the compositions which I have described.

Where an improved polish is desired, I incorporate an abrasive in the composition. The abrasive selected must be both soft and chemically inert. I refer to use infusorial earth or some other orm of silica, although it is to be understood that any suitable material may be used.

The salt and abrasive, where used, may be incorporated in the mixture during the grinding and mixing operations, or may be added after these steps have been accomplished. In the latter case, a simple mixing will generally suffice to disperse them thoroughly throughout the mixture. An intimate dispersion of the salt and abrasive is preferred in order to secure the optimum results with a minimum of material.

As I have intimated hereinbefore, one of the outstanding disadvantages of the use of compounds suggested for use as cleaners has been the unpleasant odor of the hydrogen sulfide given off during the cleaning or detarnishing process. I overcome this disadvantage by the addition of a metal or metal compound, or any suitable chemical reagent which will react with the hydrogen sulfide as it is formed. Another method of eliminating the odor of hydrogen sulfide is the, addition of a masking perfume such as an essential oil or like odori-ferous compound.

To accomplish the removal of the hydrogen sulfide I incorporate with the metal-acid composition a small quantity of a substance which is adapted to react with the gas to form an odorless compound which has no deleterious effect on the surface of the metal under treatment. I have found that-the metals or their oxides which form sulfides insoluble in dilute acids, are effective in preventing the escape of hydrogen sulfide, and thus act as an anti-odor. I prefer to use copper oxide in finely divided form, although other metals or their oxides having the desired properties such as lead or bismuth, .for instance, can be used.

As mentioned above in the case of the salt and abrasive additions to the mixture, the

anti-odor may be ground up with either of the reacting com onents, or preliminarily ground and addzzd in the mixing stage.

The following are preferre examples of compositions which are suitable for use in the powdered form:

In use, the substantially dry, powdered mixture of an electropositive metal, acid or acid salt, with or without any of the neutral salt, anti-odor or abrasive, above mentioned, is sprinkled on a damp cloth and applied to the article to be cleaned. The operation is very easily performed. There are no caustic alkaline materials or strong acids to corrode the hands of the user; there is no boiling up of the electrolyte; and the articles after cleaning merely require a simple rinsing in tap water to remove the reagents or they can be wiped with a damp cloth.

As noted previously, the acid or acid salt may be omitted from the composition and any of the materials mentioned (vinegar, lemon juice, sour milk), can be used to dampen the cloth upon whichthe other ingredients are sprinkled, the fundamental electrochemical reactions being unchanged.

The powdered composition can be packaged in any suitable manner. Care should be taken to have the package substantially airtight to prevent access of moisture to the ingredients. For export trade or for localities which are excessively damp, it may be desirable to omit the acid or acid salt from the composition, the user supplying such omission in the manner designated. As'examples of suitable forms of packages may be mentioned the cans used for dispensing toothcleanin'g powders and the hermetically sealed glassine packets or envelopes.

Any of the powder compositions made according to my invention may be incorporated in a suitable water-soluble vehicle to form a paste, and the resulting product put up in jars or collapsible tubes. The vehicle or binder used for carrying the powdered ingredients, prepared as above described, is incorporated therewith in any suitable machine, or the ingredients may be wet-ground in the vehicle or binder, care being taken to exclude moisture. As will be readily understood, the vehicle or binder used for carrying the powdered ingredients should be a non-aqueous, non-ionizing liquid, having a minimum of solvent action on the acid or acid salt used, and be readily miscible with water so that it may work by dilution therewith. I have found that denatured alcohol and glycerine are suitable vehicles, but I wish it to be understood that these are merely illustrative since other materials having the desired characteristics may be used.

Soap has been widely used as a vehicle for carrying powdered materials which are to be used as abrasives orthe like, but I find that it is not suitable for the purpose of my invention. This is due to the fact that the use of soap leaves an infinitely thin saponaceous film on the cleaned metal, which film exerts a deleterious effect on the metal and facilitates further tarnishing.

It will now be appreciated that I have provided a composition which is adapted for use in the detarnishing of metals, and one which obviates the necessity of using complicated apparatus or chemicals. The simplicity of operation,'and freedom from odors and mussiness which characterizes theuse of thecompositions comprised within the spirit and scope of my invention is a distinct advance over the practice of the prior art.

While I have disclosed preferred embodiments of my invention, I wish it to be understood that these are but preferred embodiments which typify others in which may be incorporated the underlying features of this invention. Modifications may be made in the proportions of the ingredients used, within the spirit and scope of my invention, and such modifications are intended to be covered by the appended'claims.

This application is a division of my application for metal cleaning compounds, Serial N 0. 218,115, filed September 7 1927.

I claim:

1. A potentially reactive dry composition of matter for detarnishing silver comprising commi'nuted zinc having a solid acid intimately incorporated therewith.

2. A potentially reactive composition of matter for cleaning silver comprising an intimate mixture of finely divided zinc and a solid acid dispersed in a non-aqueous vehicle.

3. A potentially reactive composition of matter for detarnishing silver comprising an intimate mixture of finely divided zinc and a solid acid dispersed in a non-aqueous, nonsaponaceous vehicle.

4. A silver cleaning composition comprising an intimate mixture of finely divided zinc, an acid and copper oxide.

5. A cleaning composition for silver-like metals comprising an intimate mixture of finely divided zinc, an acid, and copper oxide in a non-aqueous vehicle.

6. A cleaning composition for tarnishable metals, comprising an intimate mixture of finely divided zinc, an acid salt and a substance which will react with hydrogen 'sulphide to form a substantially inodorous compound.

7. A potentially reactive mix adapted .to form an electrolytic cleaner upon the addition of an aqueous solution of an acid, comprising finely divided zinc and a substance which will react with h drogen sulphide to form substantially ino orous compounds.

8. A potentially reactive mix adapted to form an electrolytic cleaner upon the addition of a suitable acid, comprising finely divided zinc and copper oxide.

9. A silver cleaning composition comprising an intimate and potentially reactive mixture of finely divided zinc and an acid salt whose aqueous solution gives an acid reaction.

GRINNELL JONES. 

